Oil-based pigmented ink composition

ABSTRACT

An oil-based pigmented ink composition containing a pigment, a polymer and an organic solvent, wherein the organic solvent contains a (poly)alkylene glycol derivative in an amount of 30 to 90% by weight and a nitrogen-containing heterocyclic compound in an amount of 1 to 30% by weight, each based on the whole weight of the ink composition, and the ink composition has a flash point of at least 63° C.

This Non-provisional application claims priority under 35 U.S.C. §119(a) on Patent Application No(s). 2003-167331 filed in Japan on Jun.12, 2003, the entire contents of which are hereby incorporated byreference.

FIELD OF THE INVENTION

The present invention relates to an oil-based pigment compositioncomprising a pigment, a polymer (a pigment-dispersant and/or a fixingresin), and an organic solvent, in particular, an oil-based pigmentcomposition for ink-jet printing systems.

PRIOR ART

In an ink-jet printing system, a liquid ink is ejected from a nozzletowards a recording medium using a pressure, heat or an electric fieldas a driving source to print the recording medium. The ink-jet printingsystem can be used with a low running cost and form high quality images.Furthermore, this printing system can use various inks such as aqueousand oil-based inks. Accordingly, the ink-jet printing system has beenexpanding its market.

Under such circumstances, large-size inkjet printers, which can be usedto print a sheet of the A-0 size with aqueous pigmented inks, have beendeveloped, and are used to output indoor posters, CAD (computer aideddrawing) drawings, or proofing for color matching in printing. Theprinted materials can be used outdoors with laminating them.

Furthermore, the demand for outdoor use of the ink-jet printed materialshas been increased. Therefore, oil-based pigmented inks are developed,which can be printed directly on films of polyvinyl chloride (PVC) andused outdoors without lamination, and have good water resistance andweather resistance.

Since the oil-based pigmented inks comprise organic solvents assolvents, they do not cause the cockling of a paper sheet in comparisonwith aqueous pigmented inks, or require no lamination of a film having areceptive layer. Therefore, they can be printed on a substrate at lowcost.

For example, JP-A-10-077432 discloses an oil-based pigmented inkcomprising a glycol solvent having a boiling point of at least 150° C.and a specific polyester resin. However, since this ink does not containa solvent in which polyvinyl chloride dissolves, it is not well fixed ona film of, for example, PVC.

JP-A 2002-302629 discloses an oil-based pigmented ink comprising asolvent having a boiling point of at least 200° C. and a specific resin.However, when a glycol solvent having a boiling point of at least 200°C. is used as a single solvent, the ink has low fixing properties on aPVC film. When a ketone solvent is used, the ink has problems such thatit is flammable or it emits a foul odor.

Apart from those oil-based pigmented inks, as an aqueous pigmented inkcomprising an aqueous solvent, JP-A 2002-363468 discloses an aqueouspigmented ink comprising N-methyl-2-pyrrolidone as a humectant. However,this aqueous ink may not be well fixed on a film of, for example, PVC.

SUMMARY OF THE INVENTION

An object of the present invention is to provide an oil-based pigmentedink, which has high safeness and low odor which are important for anoil-based pigmented ink, can be printed on an inexpensive printingmedium such as a PVC film having no receptive layer, and can endureoutdoor environment.

To achieve the above object, an extensive study has been made and it hasbeen found that when a (poly)alkylene glycol derivative and anitrogen-containing heterocyclic compound such asN-methyl-2-pyrrolidone, N-ethyl-2-pyrrolidone, etc. are used incombination as the organic solvents of an oil-based pigmented inkcomposition, the ink composition has high safeness and low odor, can beprinted on an inexpensive printing medium such as a PVC film having noreceptive layer, and can satisfactorily endure outdoor environment, andin particular, the ink composition is suitable for ink-jet printingsystems.

Accordingly, the present invention provides an oil-based pigmented inkcomposition comprising a pigment, a polymer and an organic solvent,wherein the organic solvent contains a (poly)alkylene glycol derivativein an amount of 30 to 90% by weight and a nitrogen-containingheterocyclic compound in an amount of 1 to 30% by weight, each based onthe whole weight of the ink composition, and the ink composition has aflash point of at least 63° C.

Since the oil-based pigmented ink composition of the present inventioncontains the (poly)alkylene glycol derivative and thenitrogen-containing heterocyclic compound such asN-methyl-2-pyrrolidone, N-ethyl-2-pyrrolidone, etc. in combination asthe organic solvent, the odor, which is one of the problems of theconventional oil-based pigmented ink compositions, can be improved, theink composition can be printed with good fixing and drying properties ona film of PVC having no receptive layer. Furthermore, the inkcomposition of the present invention can form a printed material havinggood resistance to water and alcohol. In particular, the ink compositionof the present invention is suitable for ink-jet printing systems. Sincethe ink composition of the present invention has a flash point of atleast 63° C., it can reduce the danger in transportation and handling.

DETAILED DESCRIPTION OF THE INVENTION

In the oil-based pigmented ink composition of the present invention, theorganic solvents essentially contain a (poly)alkylene glycol derivativeand a nitrogen-containing heterocyclic compound.

When the ink composition containing the above combination of thesolvents is printed on a printing medium having no ink-receptive layer,in particular, the PVC film, the solvents partly dissolve PVC and thusthe fixing of the ink on the film is enhanced. In addition, most of thenitrogen-containing heterocyclic compounds do not violate the regulationfor preventing poisoning with organic solvents in the Industrial Safetyand Health Law so that they are very safe, and they have low odor.Accordingly, the ink composition containing the nitrogen-containingheterocyclic compound has high safeness and low odor.

Examples of solvents in which PVC dissolves include ketones (e.g.acetone, methyl ethyl ketone, cyclohexanone, etc.), oxygen-containingheterocyclic compounds (e.g. tetrahydrofuran, etc.), nitrogen-containingheterocyclic compounds (e.g. pyrrolidone, etc.), and so on.

Among them, the ketones and tetrahydrofuran have good PVC-dissolvingpower. However, acetone, methyl ethyl ketone, methyl isobutyl ketone,methyl n-butyl ketone, cyclohexanone, methylcyclohexanone,tetrahydrofuran, etc. are designated in the Industrial Safety and HealthLaw. A material containing 5% by weight or more of one of them can behandled by a person having a special qualification, and a person whohandles such a material should get a medical checkup. Therefore, thehandling of those solvents is troublesome.

Among the ketones and tetrahydrofuran derivatives other than the abovecompounds, ketones and tetrahydrofuran derivatives having a lowmolecular weight may well dissolve PVC, but many of them have a lowflash point so that it is highly possible that ink compositionscomprising such solvents have a flash point of lower than 63° C.Furthermore, since such solvents have strong odor, the ink compositioncontaining only a slight amount of the solvent may emit odors. Ketonesand tetrahydrofuran derivatives having a high molecular weight have ahigh flash point and low odor. However, such solvents less dissolve PVCand thus the pigments in the ink composition may not be sufficientlyfixed to the substrate.

The nitrogen-containing heterocyclic compounds are heterocycliccompounds having at least one nitrogen atom in a ring, and most of themdo not violate the regulation for preventing poisoning with organicsolvents in the Industrial Safety and Health Law as described above.Therefore, they are highly safe, and emit less odor. Accordingly, inkcompositions comprising such heterocyclic compounds have good safenessand low odor. That is, the nitrogen-containing heterocyclic compoundshave much better properties as organic solvents of the ink compositionsthan the oxygen-containing heterocyclic compounds such as ketones ortetrahydrofuran.

Examples of the nitrogen-containing heterocyclic compounds include2-pyrrolidone and its derivatives, in particular, N-alkyl-2-pyrrolidonesuch as N-methyl-2-pyrrolidone, N-ethyl-2-pyrrolidone,N-(2-hydroxyethyl)-2-pyrrolidone, N-cyclohexyl-2-pyrrolidone,N-octyl-2-pyrrolidone, N-dodecyl-2-pyrrolidone, N-vinyl-2-pyrrolidone,etc.

Among them, N-methyl-2-pyrrolidone and N-ethyl-2-pyrrolidone arepreferable, since they have low odor and good fixing properties.

The nitrogen-containing heterocyclic compound is usually contained in anamount of 1 to 30% by weight, preferably 5 to 28% by weight, morepreferably 15 to 25% by weight, based on the whole weight of the inkcomposition. When the amount of the nitrogen-containing heterocycliccompound is less than 1% by weight, the ink composition may notsufficiently dissolve PVC. When the amount of the nitrogen-containingheterocyclic compound exceeds 30% by weight, the effect to dissolve PVCwill be saturated, and the volatility of the ink composition becomesinsufficient so that printed characters or images tend to drip or blur.

To qualitatively and quantitatively analyze the nitrogen-containingheterocyclic compound in the ink composition, gas chromatographic massspectroscopy (GCMS) is advantageously used.

The (poly)alkylene glycol derivative, which is another essentialcomponent of the organic solvent according to the present invention, hasa polar group (i.e., an ester group and an ether group) and ahydrophobic group (i.e., an alkyl group) in the molecule. Therefore,when the (poly)alkylene glycol derivative is used as one of the primarysolvents, it is possible to formulate an ink composition which exhibitsgood fixing properties and water resistance not only on the PVCsubstrate but also any other printing medium such as a plain paper, amatte paper, a glossy paper, etc. The fixing properties, waterresistance as well as the odor and flash point of the ink compositioncan be easily controlled by selecting the number of the ester and ethergroups and the number of carbon atoms in the alkyl group.

In view of the safeness and odor of the ink composition, the(poly)alkylene glycol derivative preferably has a flash point of 70 to120° C., more preferably 80 to 100° C., and preferably a boiling pointof 170 to 250° C.

When the (poly)alkylene glycol derivative is used in combination withthe nitrogen-containing heterocyclic compound, the flash point of theink composition as a whole can be easily set to 63° C. or higher so thatthe ink composition has very high safeness with regard to the ignitionduring transportation of the ink composition.

Examples of the (poly)alkylene glycol derivative include compoundshaving one free hydroxyl group such as a monoalkyl ether or a monoalkylester of a (poly)alkylene glycol, etc., and compounds having no freehydroxyl group such as a monoalkyl ether monoalkyl ester, a dialkylether or a dialkyl ester of a (poly)alkylene glycol, etc.

Among them, the compounds having no hydroxyl group such as the monoalkylether monoalkyl ester, the dialkyl ether and the dialkyl ester arepreferable since they can decrease the viscosity of the ink compositionand improve the water resistance of the ink composition. Among the alkylesters, those having a methyl ester group are preferable.

Examples of the monoalkyl ether monoalkyl ester of a (poly)aklyleneglycol include ethylene glycol monoalkyl ether monoalkyl ester,diethylene glycol monoalkyl ether monoalkyl ester, triethylene glycolmonoalkyl ether monoalkyl ester, propylene glycol monoalkyl ethermonoalkyl ester, dipropylene glycol monoalkyl ether monoalkyl ester,tripropylene glycol monoalkyl ether monoalkyl ester, and so on.

Among them, di- or trialkylene glycol monoalkyl ether monoalkyl ester ispreferable since it has a larger molecular weight, a higher flash pointand boiling point, and lower odor than monoalkylene glycol monoalkylether monoalkyl ester.

In particular, diethylene glycol monoalkyl ether monoalkyl ester anddipropylene glycol monoalkyl ether monoalkyl ester are preferably usedsingly or as a mixture of them.

Since these compounds have a moderate molecular weight, they have thesafeness and prevent the clogging of nozzles due to the drying of theink composition at the same time. They have no unpleasant odor andtherefore the ink composition comprising such solvents has no unpleasantodor.

Furthermore, the dipropylene glycol derivatives have better safeness andthus more suitable for use in the ink composition than the diethyleneglycol derivatives.

Specific examples of such glycol derivatives include diethylene glycolmonoethyl ether monomethyl ester, diethylene glycol monobutyl ethermonomethyl ester, diproyplene glycol monomethyl ether monomethyl ester,dipropylene glycol monoethyl ether monomethyl ester, etc.

The above derivatives are preferably used since they have a particularlyhigh flash point. In particular, dipropylene glycol monomethyl ethermonomethyl ester is preferable as a solvent of the ink compositionaccording to the present invention, since it has a high flash point andlow odor.

Examples of the dialkyl ether of a (poly)alkylene glycol includeethylene glycol dialkyl ether, diethylene glycol dialkyl ether,triethylene glycol dialkyl ether, propylene glycol dialkyl ether,dipropylene glycol dialkyl ether, tripropylene glycol dialkyl ether,etc. They may be used singly or as a mixture of two or more of them.

Specific examples of such dialkyl ethers of a (poly)alkylene glycolinclude ethylene glycol dibutyl ether, diethylene glycol dimethyl ether,diethylene glycol diethyl ether, diethylene glycol dibutyl ether,propylene glycol dimethyl ether, propylene glycol diethyl ether,propylene glycol dibutyl ether, dipropylene glycol dimethyl ether,dipropylene glycol diethyl ether, etc. These derivatives haveparticularly low odor.

Among them, (poly)propylene glycol dialkyl ethers are preferably used asthe solvents of the ink composition according to the present invention,since they have relatively low odor and a low viscosity.

Examples of the dialkyl ester of (poly)alkylene glycol include ethyleneglycol dialkyl ester, diethylene glycol dialkyl ester, triethyleneglycol dialkyl ester, propylene glycol dialkyl ester, dipropylene glycoldialkyl ester, tripropylene glycol dialkyl ester, etc. They may be usedsingly or as a mixture of two or more of them.

Preferable examples of such dialkyl esters of a (poly)alkylene glycolinclude ethylene glycol dimethyl ester, diethylene glycol, dimethylester, propylene glycol dimethyl ester, dipropylene glycol dimethylester, etc., since they have low odor.

Among them, propylene glycol dimethyl ester is preferably used as thesolvent of the ink composition according to the present invention, sinceit has relatively low odor and a low viscosity.

The (poly)alkylene glycol derivatives may be used singly or as a mixtureof two or more of them. One or more (poly)alkylene glycol derivativesare contained in the ink composition in an amount of 30 to 90% byweight, preferably 50 to 90% by weight.

To qualitatively and quantitatively analyze the (poly)alkylene glycolderivative in the ink composition, gas chromatographic mass spectroscopy(GCMS) is advantageously used.

Optionally, a (poly)alkylene glycol derivative having a flash point oflower than 63° C. may be used. Such a (poly)alkylene glycol derivativeis used in combination with the other (poly)alkylene glycol derivativein an amount such that the ink composition as a whole has a flash pointof at least 63° C. For example, when a (poly)alkylene glycol derivativehaving a flash point of 50 to 63° C., it is used in an amount of 35% byweight or less, preferably 30% by weight or less based on the wholeweight of the ink composition.

The ink composition of the present invention contains the (poly)alkyleneglycol derivative and the nitrogen-containing heterocyclic compound asthe essential organic solvents. Apart from these essential organicsolvents, the ink composition of the present invention may optionallycontain other general organic solvents such as alcohols, ketones,esters, amines, glycols, glycol ethers, aromatic compounds, etc. Thekind and amount of such an optional organic solvent should be selectedso that the characteristic properties of the ink composition of thepresent invention are not impaired.

In particular, most of the ketones, esters and aromatic compounds emitodor even if they are used in a small amount. Therefore, when such asolvent is used, one having a boiling point of at least 150° C. and aflash point of at least 70° C. is preferably used. Since anorganicsolvent having a boiling point lower than 150° C. emits odor, its amountis preferably less than 1% by weight, more preferably less than 0.5% byweight, most preferably less than 0.1% by weight based on the wholeweight of the ink composition.

The oil-based pigmented ink composition of the present invention ischaracterized in that the composition as a whole has a flash point of atleast 63° C., preferably at least 70° C. by the use of the specificcombination of the organic solvents. When an ink composition has a flashpoint of 62° C. or lower, it is classified into flammable liquids havinga high flash point in the case of dangerous materials to be shippedaccording to international transport-related laws. Therefore, thehandling of such ink compositions is difficult because of the limitationof the transport or transfer. Furthermore, such ink composition maycarry a lot of risk such as firing in the case of troubles, for example,the leakage of the ink composition. In contrast, when the inkcomposition has a flash point of 63° C. or higher, such problems can beavoided. When the ink composition has a flash point of 70° C. or higher,it is designated as Hazardous Material Group IV, Third Petroleum Oil,which is listed in the Appendix to the Fire Defense Law in Japan. Thus,its handling is easy and the dangers such as firing are suppressed, inview of the restrictions encountered in the production, storage,transport and the like.

The oil-based pigmented ink composition of the present inventioncontains one or more pigments as coloring agents in view of lightstability. The pigments include inorganic pigments and organic pigments.The pigments may be modified to increase the dispersibility thereof. Forexample, modified pigments having a dialkylaminomethyl group ordialkylaminoethylsulfonic acid amide group are preferably used.

Examples of the inorganic pigment include titanium oxide, Chinese white(zinc flower), zinc oxide, lithopone, iron oxide, aluminum oxide,silicon dioxide, kaolinite, montmorillonite, talc, barium sulfate,calcium carbonate, cadmium red, red oxide, molybdenum red, chromevermilion, molybdate orange, chrome yellow, cadmium yellow, yellow ironoxide, chromium oxide, viridian, cobalt green, titanium cobalt green,Paris blue, cobalt chrome green, Armenian blue, ultramarine bluepigment, cobalt blue, cerulean blue, manganese violet, cobalt violet,mica, etc. Also, carbon black comprising acidic, neutral or basic carbonmay be used.

Examples of the organic pigments include azo pigments, azomethinepigments, polyazo pigments, phthalocyanine pigments, quinacridonepigments, anthraquinone pigments, indigo pigments, thioindigo pigments,quinophthalone pigments, benzimidazolone pigments, isoindoline pigments,isoindolione pigments, etc. In addition, hollow particles of crosslinkedacrylic resins may be used as a pigment.

Examples of pigments contained in cyan ink compositions include C.I.Pigment Blue 1, 2, 3, 15:3, 15:4, 15:34, 16, 22 and 60, etc. Inparticular, one or more of C.I. Pigment Blue 15:3 and 15:3 arepreferably used in view of their good weather resistance and coloringpower.

Examples of pigments contained in magenta ink compositions include C.I.Pigment Red 5, 7, 12, 48 (Ca), 48 (Mn), 57 (Ca), 57:1, 112, 122, 123,168, 184, 202, 209 and 254, C.I. Pigment Violet 19, etc. In particular,one or more of C.I. Pigment Red 122, 202, 209 and 254 and C.I. PigmentViolet 19 are preferably used in view of their good weather resistanceand coloring power.

Examples of pigments contained in yellow ink compositions include C.I.Pigment Yellow 1, 2, 3, 12, 13, 14C, 16, 17, 73, 74, 75, 83, 93, 95, 97,98, 109, 110, 114, 120, 128, 129, 130, 138, 139, 147, 150, 151, 154,155, 180, 185, 213, 214, etc. Among them, C.I. Pigment Yellow 74, 83,109, 110, 120, 128, 138, 139, 150, 151, 154, 155, 213 and 214 arepreferably used singly or as a mixture thereof in view of their goodweather resistance.

Examples of pigments contained in black ink compositions include HCF,MCF, RCF, LEF and SCF (available from Mitsubishi Chemical Co., Ltd.),MONARCH and REGAL (available from Cabot, USA), COLOR BLACK, SPECIALBLACK and PRINTEX (available from Degussa Huls AG), TOKA BLACK(available from TOKAI CARBON Co., Ltd.), RAVEN (available from ColumbianChemical, USA), and the like.

In particular, one or more of HCF #2650, #2600, #2350 and #2300, MCF#1000, #980, #970 and #960, MCF 88, LFFMA 7, MA 8, MA 11, MA 77 and MA100 (available from Mitsubishi Chemical Co., Ltd.), and PRINTEX 95, 85,75, 55 and 45 (available from Degussa Huls AG) are preferably used.

In the oil-based pigmented ink composition of the present invention,polymer are used as a pigment-dispersant and/or a fixing resin. Thepigment-dispersant has good affinity with the pigment and stabilizes thedispersion of the pigment. The fixing resin has good adhesion to asubstrate and imparts durability to the printed material.

When the pigment-disperstant and/or the fixing resin are adequatelyselected depending on the kinds of the pigment, organic solvents andprinting medium, the ink composition has good effects. Among thepolymers, a single polymer may act as a pigment-dispersant and a fixingresin.

The polymer preferably has a solubility in water and ethanol of 3% byweight or less, more preferably 1% by weight or less.

The pigment-dispersant and the fixing resin remain on the surface of thesubstrate after printing with the ink-jet printing system and then theyare dried and fixed to the substrate. Therefore, if the polymer iseasily soluble in water, the printed material has less water resistanceso that the printed characters and/or images are washed off with rain,when the printed material is used outdoors. When the printed material isused in the form of a poster, a coating agent is often sprayed on theprinted surface. Since the coating agent usually contains an alcoholicsolvent as a primary solvent, the printed characters and images aresagged with the coating agent if the polymers are easily soluble in thealcoholic solvent.

In contrast, the polymers having the solubility in water and ethanol inthe above range do not suffer from such problems.

As the pigment-dispersant, an ionic or nonionic surfactant, or ananionic, cationic or nonionic polymer is used. In view of the dispersionstability, water resistance and the durability of the printed materialsuch as scratch resistance, etc, the polymer, in particular, a polymerhaving a cationic group or an anionic group is preferable.

The pigment-dispersant stabilizes the pigment in the organic solventthrough an acid-base interaction between the pigment and the dispersant.Thus, the pigment-dispersant should contain at least one of a cationicgroup and an anionic group, which function as pigment-absorbing sites,and the kind and amount of the cationic group and the anionic group ofthe dispersant are selected depending on the kind of the pigment.

Examples of the polymeric pigment-dispersant include SOLSPERSE(available from Zeneca), DISPER BYK (available from BYK-Chemie), EFKA(available from EFKA Additives), etc. Among them, DISPER BYK 161, 162and 168, and EFKA 4050, 4055 and 4060 are preferable. When thesepigment-dispersants are selected and used according to the kinds of thepigment and solvents, the ink composition can often exhibit goodeffects.

The pigment-dispersants are usually available in the market in the formof solutions. In such a case, the solution contains a low-boilingsolvent such as toluene, xylene, ethyl acetate, butyl acetate, methylethyl ketone, etc. When the solution is used as such in the preparationof the ink composition, the ink composition may have odor originatedfrom such a solvent. Therefore, the low-boiling solvent is removed fromthe solution of the pigment-dispersant, if necessary, when the solventsmay have adverse affects on the properties of the ink composition, forexample, odor, safeness, etc. The low-boiling solvent can be removed byvacuum distillation, reprecipitation, etc.

By such removal methods, the content of the low-boiling solvent in thedispersant solution, in particular, a solvent having a boiling point of170° C. or lower, is decreased to 1% by weight or lower, preferably 0.5%by weight or lower, more preferably 0.1% by weight or lower of thedispersant solution. Thereby, the odor of the ink composition can becontrolled.

Examples of the fixing resin include acrylic resins, polyester resins,polyurethane resins, vinyl chloride resins, cellulose resins (e.g.nitrocellulose), and the like. Most of these resins have good fixingproperties to PVC. The water resistance, dispersion stability, printingproperties, etc. can be controlled by selecting the functional groupsand structures of the resins.

Examples of the acrylic resin include JOHNCRYL of Johnson Polymer andS-LEK of Sekisui Chemical Co., Ltd. Examples of the polyester resininclude ELITEL of UNITIKA Co., Ltd. and VYLON of Toyobo Co., Ltd.Examples of the polyurethane resin include VYLON UR of Toyobo Co., Ltd.,NT-HiLamic of Dainichi Seika Color & Chemicals Mfg. Co., Ltd., CRISVONof Dainippon Ink and Chemicals Incorporated, and NIPPORAN of NipponPolyurethane Industry Co., Ltd. Examples of the vinyl chloride resininclude SOLBIN of Nissin Chemical Industries, Ltd., SEKISUI PVC-TG andSEKISUI PVC-HA of Sekisui Chemical Co., Ltd., and UCAR Series of DOWCHEMICAL. Examples of nitrocellulose include HIG, LIG, SL and VX ofASAHI CHEMICAL Co., Ltd. and NITROCELLULOSE RS and SS of DAICEL CHEMICALINDUSTRIES, LTD.

Among them, the polyurethane resins, polyester resins, vinyl chlorideresins and nitrocellulose are preferable.

The fixing resin preferably has a weight average molecular weight of2000 to 100,000, more preferably 5000 to 80,000, most preferably 10,000to 50,000.

When the weight average molecular weight of the fixing resin is lessthan 2000, the effect of steric repellence may not be achieved when theanionic resin is adsorbed on the pigment particles in the inkcomposition so that the storage stability of the ink composition is notimproved, the fixing of the pigment to the printing medium may not beincreased, and thus the film strength may not be sufficiently attained.When the weight average molecular weight of the fixing resin exceeds100,000, the effects of the use of the fixing resin is saturated andalso the viscosity of the ink composition increases so that the inkcomposition may not have sufficient flowability.

Herein, the weight average molecular weight means a molecular weight ofthe resin measured by gel permeation chromatography and calibrated withstandard samples of polystyrene.

When the polymeric a pigment-dispersant is present in the inkcomposition of the present invention, the amount of thepigment-dispersant may depend on the kinds of the pigment and solventused for dispersing the pigment, the dispersing conditions, etc., and isusually from 5 to 150% by weight, in particular, from 40 to 150% byweight when the organic pigment is used, and from 5 to 60% by weightwhen the inorganic pigment is used, based on the weight of the pigment.

When the polymeric fixing resin is present in the ink composition of thepresent invention, the amount of the fixing resin may depend on the kindand molecular weight of the resin, the kinds of the pigment andsolvents, and is usually from 5 to 200% by weight based on the weight ofthe pigment.

The ink composition of the present invention can be prepared by anyconventional method. For example, the pigment, the polymer(pigment-dispersant) and the (poly)alkylene glycol derivative as a partof the solvents are premixed and dispersed. Then, to the dispersion, thepolymer (fixing resin), the rest of the (poly)alkylene glycol derivativeand the nitrogen-containing heterocyclic compound are added and mixed todisperse the pigment and the polymers in the solvents.

To prepare the above dispersion, the components are well stirred andmixed using a barrel-driving type mills (e.g. ball mill, centrifugalmill, planetary mill, etc.), high-speed rotation mills (e.g. sand mill,etc.), medium-agitation mills (e.g. agitated vessel mill, etc.), simpledispersing equipment (e.g. disper, etc.), and the like.

After the formation of the dispersion, the dispersion may additionallybe uniformly mixed with a simple stirrer such as a three-one motor, amagnetic stirrer, a disper, a homogenizer, etc. Furthermore, to reducethe particle size of the solid components, the dispersion may optionallybe mixed with a dispersing equipment such as a bead mill, a highpressure jet mill, etc.

Besides the pigment, polymers and organic solvents, the ink compositionof the present invention may optionally contain conventionally usedadditives such as surfactants, surface-modifiers, leveling agents,defoaming agents, antioxidants, pH regulators, charging agents,disinfectants, preservatives, deodorants, charge-adjusters, wettingagents, anti-skinning agents, UV-ray absorbers, perfumes, pigmentderivatives, etc.

The oil-based pigmented ink of the present invention, in particular, onefor ink-jet printing systems, has a surface tension of 20 to 40 mN/m (at25° C.) and a viscosity of 2 to 15 cp (at 25° C.), preferably 3 to 13cp, more preferably 4 to 12 cp.

When the ink composition having the surface tension and viscosity in theabove ranges is used in the ink-jet printing system, it has good jettingproperties so that the flying track of an ink drop is not curved orswerved, and the printed characters or images are not or hardly blurred,when the ink composition is printed on a plain paper or a matte paper,etc.

In the oil-based pigmented ink composition of the present invention, thepigment preferably has a dispersion average particle size of 20 to 200nm, more preferably 50 to 160 nm. When the dispersion average particlesize is less than 20 nm, the particles are too small so that the printedmaterial may lose the durability. When the dispersion average particlesize exceeds 200 nm, the fineness of the printed material maydeteriorate.

With the oil-based pigmented ink composition of the present invention,the surface tension and viscosity at 25° C. and the dispersion averageparticle size and maximum dispersion particle size of the pigment can beadjusted in the above respective ranges by suitably selecting the kindsand amounts of the components of the ink composition, since the abovespecific compounds are used as the organic solvents.

The oil-based pigmented ink composition of the present invention has lowodor and high safeness, is printable on various printing media such asan inexpensive film of PVC having no receptive layer and can endure theoutdoor use conditions. Furthermore, the oil-based pigmented inkcomposition of the present invention is advantageously used in theink-jet printing systems. In such systems, the four or more inkcompositions including the cyan, magenta, yellow and black inkcompositions can be used at the same time to form images.

EXAMPLES

Hereinafter, the present invention will be illustrated by the followingexamples, in which “parts” means “parts by weight” unless otherwiseindicated.

In the Examples, a pigment-dispersant “BYK 161” and a fixing resin“Vylon UR-8300” were used after removing low boiling solvents by vacuumdistillation and then diluting them with organic solvents to be used ina dispersing step to a solid content of 20% by weight.

In the Examples, the amounts of pigment-dispersants “BYK 161” and“SOLSPERSE 13940” and a fixing resin “Vylon UR 8300” are expressed interms of weights after being diluted with organic solvents.

Example 1

In a 100 cc plastic bottle, 4 parts of a copper phthalocyanine bluepigment (“FASTOGEN BLUE 5430SD” available from Dainippon Ink andChemicals Incorporated), 10 parts of a pigment-dispersant (“BYK 161”, anamine-based polymeric dispersant, available from BYK-Chemie), 6 parts ofdipropylene glycol monomethyl ether monomethyl ester (available from DowChemical; flash point: 96° C.) as an organic solvent and 100 parts ofzirconia beads having a diameter of 0.3 mm were weighed and charged.Then, the mixture was dispersed with a paint conditioner (available fromTOYO SEIKI KOGYO Co., Ltd.) for 2 hours.

Then, 7.5 parts of the dispersion prepared in the previous step, 3.8parts of a polyurethane resin (“Vylon UR 8300” available from TOYOBOCo., Ltd.), 10 parts of N-methyl-2-pyrrolidone, 18.7 parts ofdipropylene glycol monomethyl ether monomethyl ester and 10 parts ofdipropylene glycol dimethyl ether (available from Dow Chemical; flashpoint: 60° C.) were added, and the mixture was stirred with a magneticstirrer for 30 minutes. Thereafter, the mixture was suction filtratedthrough a glass filter (available from KIRIYAMA GLASS WORKS Co., Ltd.)to obtain an oil-based pigmented ink composition (hereinafter referredto as Ink Composition A).

Example 2

A dispersion was prepared in the same manner as in Example 1 except thata quinacridon pigment (“HOSTAPERM PINK EB trans” available from ClariantAG) was used in place of the copper phthalocyanine pigment, and 20 partsof the pigment-dispersant “BYK 161” and 6 parts of dipropylene glycolmonomethyl ether monomethyl ester were used. Then, using thisdispersion, an oil-based pigmented ink composition (Ink Composition B)was prepared in the same manner as in Example 1.

Example 3

A dispersion was prepared in the same manner as in Example 1 except thatan azo pigment (“NOVOPERM Yellow H2G” available from Clariant AG) wasused in place of the copper phthalocyanine pigment. Then, using thisdispersion, an oil-based pigmented ink composition (Ink Composition C)was prepared in the same manner as in Example 1.

Example 4

A dispersion was prepared in the same manner as in Example 1 except thatan acidic carbon black pigment (“MA 8” available from MITSUBISHICHEMICAL CORPORATION) was used in place of the copper phthalocyaninepigment. Then, using this dispersion, an oil-based pigmented inkcomposition (Ink Composition D) was prepared in the same manner as inExample 1.

Example 5

A dispersion was prepared in the same manner as in Example 2 except thata quinacridon pigment (“Chromofine Magenta 6887” available from DainichiSeika Color & Chemicals Mfg. Co., Ltd.) was used in place of thequinacridone pigment “HOSTAPERM PINK EB trans”.

Then, to 7.5 parts of the dispersion prepared in the previous step, 0.6part of nitrocellulose (“RS 1/4” available from DAICEL CHEMICALINDUSTRIES, LTD.), 10 parts of N-methyl-2-pyrrolidone, 21.9 parts ofdipropylene glycol monomethyl ether monomethyl ester and 10 parts ofdipropylene glycol dimethyl ether were added, and the mixture wasstirred with a magnetic stirrer for 30 minutes. Thereafter, the mixturewas suction filtrated through a glass filter to obtain an oil-basedpigmented ink composition (Ink Composition E).

Example 6

A dispersion was prepared in the same manner as in Example 1 except thatan azo pigment (“YELLOW PIGMENT E4GN-GT” available from Bayer AG) wasused in place of the copper phthalocyanine pigment, and 20 parts of thepigment-dispersant “BYK 161” and 6 parts of dipropylene glycolmonomethyl ether monomethyl ester were used.

Then, to 7.5 parts of the dispersion prepared in the previous step, 0.8part of a polyester resin (“ELITEL UE-9800” available from UNITIKA Co.,Ltd.; weight average molecular weight: 13,000), 10 parts ofN-methyl-2-pyrrolidone, 21.7 parts of dipropylene glycol monomethylether monomethyl ester, and 10 parts of dipropylene glycol dimethylether were added, and the mixture was stirred with a magnetic stirrerfor 30 minutes. Thereafter, the mixture was suction filtrated through aglass filter to obtain an oil-based pigmented ink composition (InkComposition F).

Example 7

A dispersion was prepared in the same manner as in Example 1 except thata basic carbon black pigment (“Printex 85” available from DEGUSSA HULS)was used in place of the copper phthalocyanine pigment, and propyleneglycol dimethyl ether (available from Dow Chemical; flash point: 93° C.)was used in place of dipropylene glycol monomethyl ether monomethylester.

Then, to 7.5 parts of the dispersion prepared in the previous step, 0.5part of a polyester resin (“Vylon 296” available from TOYOBO Co., Ltd.;weight average molecular weight: 14,000), 10 parts ofN-methyl-2-pyrrolidone, and 32 parts of diethylene glycol dibutyl ether(available from KYOWA HAKKO KOGYO Co., Ltd.; flash point: 122° C.) wereadded, and the mixture was stirred with a magnetic stirrer for 30minutes. Thereafter, the mixture was suction filtrated through a glassfilter to obtain an oil-based pigmented ink composition (Ink CompositionG).

Example 8

A dispersion was prepared in the same manner as in Example 1 except thatan amine-based polymer dispersant “BYK 168” (available from BYK-Chemie)was used in place of “BYK 161”.

Then, to 7.5 parts of the dispersion prepared in the previous step, 1.1parts of a vinyl chloride-vinyl acetate copolymer (“VROH” available fromDow Chemical; weight average molecular weight: 15,000), 10 parts ofN-methyl-2-pyrrolidone, 19.4 parts of dipropylene glycol monomethylether monomethyl ester and 12 parts of dipropylene glycol dimethyl ether(available from Dow Chemical; flash point: 60° C.) were added, and themixture was stirred with a magnetic stirrer for 60 minutes. Thereafter,the mixture was suction filtrated through a glass filter to obtain anoil-based pigmented ink composition (Ink Composition H).

Example 9

A dispersion was prepared in the same manner as in Example 1 except thatethylene glycol monobutyl ether monoethyl ester (available from KYOWAHAKKO KOGYO Co., Ltd.; flash point: 87.5° C.; boiling point: 192° C.)was used in place of dipropylene glycol monomethyl ether monomethylester.

Then, to 7.5 parts of the dispersion prepared in the previous step, 3.8parts of a polyurethane resin (“Vylon UR 8300” available from TOYOBOCo., Ltd.), 10 parts of N-methyl-2-pyrrolidone, 23.7 parts of ethyleneglycol monobutyl ether monomethyl ether, and 5 parts of dipropyleneglycol monomethyl ether monomethyl ester were added, and the mixture wasstirred with a magnetic stirrer for 30 minutes. Thereafter, the mixturewas suction filtrated through a glass filter to obtain an oil-basedpigmented ink composition (Ink Composition I).

Example 10

A dispersion was prepared in the same manner as in Example 1 except thatan azo pigment (“YELLOW PIGMENT E4GN-GT” available from Bayer AG) wasused in place of the copper phthalocyanine pigment, and 10 parts of apigment-dispersant “BYK 168” was used in place of “BYK 161”.

Then, to 7.5 parts of the dispersion prepared in the previous step, 0.8part of a vinyl chloride-vinyl acetate copolymer (“SOLBIN TA5R”available from NISSIN CHEMICAL Co., Ltd.; weight average molecularweight: 28,000), 10 parts of N-ethyl-2-pyrrolidone, 19.7 parts ofdipropylene glycol monomethyl ether monomethyl ester, and 12 parts ofdipropylene glycol dimethyl ether were added, and the mixture wasstirred with a magnetic stirrer for 30 minutes. Thereafter, the mixturewas suction filtrated through a glass filter to obtain an oil-basedpigmented ink composition (Ink Composition J).

Example 11

To 7.5 parts of the dispersion prepared in the same manner as in Example1, 3.8 parts of “Vylon UR 8300”, 5 parts of N-methyl-2-pyrrolidone, 23.7parts of dipropylene glycol monomethyl ether monomethyl ester, and 10parts of dipropylene glycol dimethyl ether were added, and the mixturewas stirred with a magnetic stirrer for 30 minutes. Thereafter, themixture was suction filtrated through a glass filter to obtain anoil-based pigmented ink composition (Ink Composition K).

Example 12

To 7.5 parts of the dispersion prepared in the same manner as in Example1, 3.8 parts of “Vylon UR 8300”, 15 parts of N-methyl-2-pyrrolidone,13.7 parts of dipropylene glycol monomethyl ether monomethyl ester, and10 parts of dipropylene glycol dimethyl ether were added, and themixture was stirred with a magnetic stirrer for 30 minutes. Thereafter,the mixture was suction filtrated through a glass filter to obtain anoil-based pigmented ink composition (Ink Composition L).

Comparative Example 1 Oil-Based Pigmented Ink Composition Comprising 50%by Weight or More of (Poly)Alkylene Glycol Derivative Having a FlashPoint Lower than 50° C.

A dispersion was prepared in the same manner as in Example 1 except thatpropylene glycol monomethyl ether monoethyl ether having a flash pointof 46.5° C. (available from KYOWA HAKKO KOGYO Co., Ltd.) was used inplace of dipropylene glycol monomethyl ether monomethyl ester.

Then, to 7.5 parts of the dispersion prepared in the previous step, 3.8parts of “Vylon UR 8300”, 10 parts of N-methyl-2-pyrrolidone, 18.7 partsof propylene glycol monomethyl ether monomethyl ester, and 10 parts ofdipropylene glycol monomethyl ether monomethyl ester were added, and themixture was stirred with a magnetic stirrer for 30 minutes. Thereafter,the mixture was suction filtrated through a glass filter to obtain anoil-based pigmented ink composition (Ink Composition M).

Comparative Example 2 Oil-Based Pigmented Ink Composition Comprising aHydrocarbon as a Primary Solvent

A dispersion was prepared in the same manner as in Example 1 except thatan aliphatic hydrocarbon solvent (“ISOPER G” available from ExxonChemical) was used in place of dipropylene glycol monomethyl ethermonomethyl ester, and an amine-based polymer dispersant (“SOLSPERSE13940” available from Zeneca) was used as a pigment-dispersant.

Then, the ink composition was prepared in the same manner as in Example1 except that 10 parts of N-dimethyl-2-pyrrolidone and 28 parts of“ISOPER G” were added to 10 parts of the dispersion prepared in theprevious step.

Comparative Example 3 Oil-Based Pigmented Ink Composition 1 Containingno N-Alkyl-2-Pyrrolidone

To 7.5 parts of the dispersion prepared in the same manner as in Example1, 0.8 part of nitrocellulose (“RS 1/4” available from DAICEL CHEMICALINDUSTRIES, LTD.), 31.7 parts of dipropylene glycol monomethyl ethermonomethyl ester, and 10 parts of dipropylene glycol dimethyl ether wereadded, and the mixture was stirred with a magnetic stirrer for 30minutes. Thereafter, the mixture was suction filtrated through a glassfilter to obtain an oil-based pigmented ink composition (Ink Composition0).

Example 4 Oil-Based Pigmented Ink Composition 2 Containing noN-Alkyl-2-Pyrrolidone

A dispersion was prepared in the same manner as in Example 1 except thatethylene glycol monobutyl ether monomethyl ester was used in place ofdipropylene glycol monomethl ether monomethyl ester.

Then, to 7.5 parts of the dispersion prepared in the previous step, 1part of a polyester resin (“Vylon 200” available from TOYOBO Co., Ltd.),and 41.5 parts of ethylene glycol monobutyl ether monomethyl ester wereadded, and the mixture was stirred with a magnetic stirrer for 60minutes. Thereafter, the mixture was suction filtrated through a glassfilter to obtain an oil-based pigmented ink composition (Ink CompositionP).

Comparative Example 5 Oil-Based Pigmented Ink Composition 3 Containingno N-Alkyl-2-Pyrrolidone

A dispersion was prepared in the same manner as in Example 1 except thatan acidic carbon black (“MA 100” available from Mitsubishi Chemical Co.,Ltd.) was used in place of the copper phthalocyanine pigment, diethyleneglycol monobutyl ether monomethyl ester (flash point: 124° C.; boilingpoint: 247° C.) was used in place of dipropylene glycol monomethyl ethermonomethyl ester, and 2.0 parts of an anionic surfactant (“HOMOGENOLL-95” available from KAO Corporation) was used as a pigment-dispersant.

Then, to 16.25 parts of the dispersion prepared in the previous step,chlorinated polyethylene (“HE-510” available from Nippon PaperIndustries Co., Ltd.), and 29.5 parts of diethylene glycol monobutylether monomethyl ester as an organic solvent were added. Thereafter, anink composition (Ink Composition Q) was prepared in the same manner asin Example 1.

Comparative Example 6 Oil-Based Pigmented Ink Composition 1 Containingno (Poly)Alkylene Glycol Derivative

A dispersion was prepared in the same manner as in Example 1 except thata quinacridon pigment (“PV Fast Red E5B” available from Clariant AG) wasused in place of the copper phthalocyanine pigment, propylene carbonate(flash point: 132° C.; boiling point: 242° C.) was used in place ofdipropylene glycol monomethyl ether monomethyl ester, and 2.0 parts of“HOMOGENOL L-95” was used as a pigment-dispersant.

Then, to 16.25 parts of the dispersion prepared in the previous step,4.25 parts of nitrocellulose (“SL-1” available from Asahi Chemical Co.,Ltd.), and 29.5 parts of propylene carbonate as an organic solvent wereadded. Thereafter, an ink composition (Ink Composition R) was preparedin the same manner as in Example 1.

Comparative Example 7 Oil-Based Pigmented Ink Composition 2 Containingno (Poly)Alkylene Glycol Derivative

A dispersion was prepared in the same manner as in Comparative Example 6except that cyclohexanone (flash point: 44° C.; boiling point: 156° C.)was used in place of propylene carbonate.

Then, to 16.25 parts of the dispersion prepared in the previous step,8.5 parts of “Vylon 200”, and 29.5 parts of cyclohexanone as an organicsolvent were added. Thereafter, an ink composition (Ink Composition S)was prepared in the same manner as in Example 1.

Comparative Example 8 Aqueous Pigmented Ink Composition Containing Waterand N-Methyl-2-Pyrrolidone as Solvents

In a 100 cc plastic bottle, 4 parts of a copper phthalocyanine bluepigment (“FASTOGEN BLUE 5430SD” available from Dainippon Ink andChemicals Incorporated), 6 parts of a pigment-dispersant (“JOHNCRYL”available from JOHNSON POLYMER CORPORATION), 10 parts of a mixture ofion-exchanged water and triethylene glycol (90:10 by weight), and 100parts of zirconia beads having a diameter of 3 mm were weighed andcharged. Then, the mixture was dispersed with a paint conditioner(available from TOYO SEIKI KOGYO Co., Ltd.) for 2 hours.

Then, to 7.5 parts of the dispersion prepared in the previous step, 10parts of N-methyl-2-pyrrolidone, and 22.5 parts of ion-exchanged waterwere added, and the mixture was stirred with a magnetic stirrer for 30minutes. Thereafter, the mixture was suction filtrated through a glassfilter to obtain an aqueous pigmented ink composition (Ink CompositionT).

With Ink Compositions A to L of Examples 1-12, Ink Compositions M to Sof Comparative Examples 1-7, and Ink Composition T of ComparativeExample 8, a viscosity, a surface tension, a dispersion average particlesize and a flash point were measured by the methods described below. Theresults are shown in Table 1.

Viscosity:

A viscosity of an ink composition was measured using a R100 viscometer(available from TOKI SANGYO Co., Ltd.) at 25° C. and a cone rotationspeed of 20 rpm.

Surface Tension:

A surface tension of an ink composition was measured using afull-automatic balance type electrotensiometer ESB-V (available fromKYOWA SCIENCE Co., Ltd.) at an ink temperature of 25° C.

Dispersion Average Particle Size:

A dispersion average particle size of pigment particles was measuredusing a particle size analyzer N4-PLUS (a laser Doppler particle sizeanalyzer available from Coulter).

Flash Point:

A flash point was measured using a SETA sealed flash point tester.

TABLE 1 Dispersion Ink Surface average Flash Example composi- Viscositytension particle point No. tion (cp) (mN/m) size (nm) (° C.) Ex. 1 A 4.529.0 98 74 Ex. 2 B 5.0 28.8 128 75 Ex. 3 C 4.3 29.1 135 74 Ex. 4 D 4.228.8 105 75 Ex. 5 E 5.2 28.8 110 74 Ex. 6 F 4.9 29.3 158 75 Ex. 7 G 5.629.5 139 102 Ex. 8 H 4.7 28.8 118 71 Ex. 9 I 4.2 28.2 104 72 Ex. 10 J5.2 28.9 148 71 Ex. 11 K 4.4 28.7 99 73 Ex. 12 L 4.7 29.3 101 75 C. Ex.1 M 3.8 26.9 104 55 C. Ex. 2 N 4.0 23.2 135 43 C. Ex. 3 O 4.1 28.4 11675 C. Ex. 4 P 3.2 29.5 115 48 C. Ex. 5 Q 11.8 29.0 187 124 C. Ex. 6 R11.5 35.0 195 132 C. Ex. 7 S 3.5 36.5 138 43 C. Ex. 8 T 3.1 36.5 128 —

As can be seen from the results in Table 1, the oil-based pigmented inkcompositions A to L according to the present invention has adequateviscosities, surface tensions and dispersion average particle sizes, andalso they have a flash point of 70° C. or higher, so that they aredesignated as Hazardous Material Group IV, Third Petroleum Oil,water-insoluble liquid, which is listed in the Appendix to the FireDefense Law in Japan, and can be relatively safely handled.

In contrast, oil-based pigmented ink compositions M, N, P and S ofComparative Examples 1, 2, 4 and 7 had a flash point lower than 70° C.,so that they are designated as Hazardous Material Group IV, SecondPetroleum Oil, water-insoluble liquid. Thus, such compositions should becarefully handled and their storage and transportation are restricted.

Next, with Ink Compositions A to L of Examples 1-12, Ink Compositions Mto S of Comparative Examples 1-7, and Ink Composition T of ComparativeExample 8, a drying property, a fixing property, alcohol resistance andodor were evaluated by the methods described below. The results areshown in Table 2.

Drying Property:

An ink composition was coated on a glossy PVC sheet (P-224RW availablefrom LINTEC Corporation) with a No. 6 wire bar (available from TOYOSEIKI KOGYO Co., Ltd.) in a temperature-controlled room at 25° C. and30% RH, and its drying property was evaluated according to the followingcriteria:

A: When the coated composition is touched with a finger, the coatedcomposition does not adhere to the finger within one minute drying.

B: When the coated composition is touched with a finger, the coatedcomposition does not adhere to the finger within 5 minutes drying.

C: When the coated composition is touched with a finger, the coatedcomposition still adheres to the finger after 5 minutes drying.

Fixing Property:

An ink composition was coated on a glossy PVC sheet (P-224RW availablefrom LINTEC Corporation) with a No. 6 wire bar (available from TOYOSEIKI KOGYO Co., Ltd.) in a temperature-controlled room at 25° C. and30% RH, and kept standing for 1 hour. After that, the surface of thecoated ink composition was scrubbed with a finger for 30 seconds. Then,the fixing property was evaluated according to the following criteria:

A: No scrubbed mark was observed.

B: A small number of scrubbed marks were observed.

C: Scrubbed marks were generated and the substrate PVC sheet wasexposed.

Alcohol Resistance:

An ink composition was coated on a glossy PVC sheet (P-224RW availablefrom LINTEC Corporation) with a No. 6 wire bar (available from TOYOSEIKI KOGYO Co., Ltd.) in a temperature-controlled room at 25° C. and30% RH, and kept standing for 1 hour. After that, the surface of thecoated ink composition was wiped with a piece of cloth (BENCOTTONavailable from ASAHI CHEMICAL Co., Ltd.) soaked with a water/ethanolmixture (weight ratio of 1:1). Then, the alcohol resistance wasevaluated according to the following criteria:

A: The surface of the coated ink composition was not wiped off.

B: When the surface of the coated ink composition was strongly wiped,the color was slightly faded.

C: The coated ink composition was easily wiped off and the substrate PVSsheet was exposed.

Odor:

An ink composition was coated on a glossy PVC sheet (P-224RW availablefrom LINTEC Corporation) with a No. 6 wire bar (available from TOYOSEIKI KOGYO Co., Ltd.) in a temperature-controlled room at 25° C. and30% RH, and kept standing for 10 minutes. Then, the odor from the coatedink composition was smelled and evaluated according to the followingcriteria:

A: Substantially no odor was smelled.

B: Slight odor was smelled.

C. Unpleasant odor was smelled.

TABLE 2 Ink Example composi- Drying Fixing Alcohol No. tion propertyproperty resistance Odor Ex. 1 A A A A A Ex. 2 B A A A A Ex. 3 C A A A AEx. 4 D A A A A Ex. 5 E A A A A Ex. 6 F A A A A Ex. 7 G A A A A Ex. 8 HA A A A Ex. 9 I A A A B Ex. 10 J A A A A Ex. 11 K B A B A Ex. 12 L B A AA C. Ex. 1 M A A A C C. Ex. 2 N C C C B C. Ex. 3 O B B B A C. Ex. 4 P BA C B C. Ex. 5 Q C C C A C. Ex. 6 R C C C A C. Ex. 7 S A A A C C. Ex. 8T C C C A

As can be seen from the results of Table 2, oil-based pigmented inkcompositions A to L of Examples 1 to 12 had good drying property, fixingproperty and alcohol resistance, and had problem-free printing propertyon PVC.

Among oil-based pigmented ink compositions A to L of Examples 1 to 12,ink composition I of Example 9 emitted slight odor and may have a smalltrouble when used in a printer. However, ink compositions A to H and Jto L of Examples 1-8 and 10 to 12 emit substantially no odor and causeno problem when used in a printer.

Since ink composition K of Example 11 contained a small amount ofN-methyl-2-pyrrolidone, it slowly interfused in PVC, had a slightly lowdrying property and did not largely dissolve PVC. Accordingly, itsalcohol resistance was not good. Ink composition L of Example 12containing a relatively large amount of N-methyl-2-pyrrolidone has goodfixing property to PVC, but N-methyl-2-pyrrolidone, which shouldinterfuse in PVC, was saturated and remained on the surface, so that itsdrying property was less satisfactory.

In contrast, ink composition M and S of Examples 1 and 7 had no problemin printing property on PVC. However, since they contained thelow-boiling solvent, they had a small problem of odor so that it maycause some trouble when used in a printer. These ink compositions had aflash point of lower than 62° C. as described above. Thus, their storageand transportation are restricted.

Ink composition N and T of Comparative Examples 2 and 8 comprising thehydrocarbon solvent did not emit odor, but had no fixing property on PVCand the ink compositions were repelled.

Furthermore, ink compositions O and P of Comparative Examples 3 and 4,which contained no N-alkyl-2-pyrrolidone, had relatively low dryingproperty since they contained no solvent that dissolves the PVCsubstrate, and they had inferior fixing property and alcohol resistanceto the ink compositions of Examples 1 to 12.

Ink composition Q of Comparative Example 5 containing noN-alkyl-2-pyrrolidone and ink composition R of Comparative Example 6containing neither N-alkyl-2-pyrrolidone nor (poly)alkylene glycolderivative contained the high-boiling solvent so that they had noproblem in their odor. However, they had low drying property and did notinterfuse in the PVC substrate. Thus, the solvents remained on thesurface of the PVC substrate, and the ink composition had poor fixingproperty and alcohol resistance.

1. An oil-based pigmented ink composition comprising a pigment, apolymer and an organic solvent, wherein the organic solvent contains a(poly)alkylene glycol derivative in an amount of 30 to 90% by weight anda nitrogen-containing heterocyclic compound in an amount of 10 to 30% byweight, each based on the whole weight of the ink composition, and theink composition has a flash point of at least 63° C.
 2. The oil-basedpigmented ink composition according to claim 1, wherein saidnitrogen-containing heterocyclic compound is a N-alkyl-2-pyrrolidone. 3.The oil-based pigmented ink composition according to claim 2, whereinsaid N-alkyl-2-pyrrolidone is at least one of N-methyl-pyrrolidone andN-ethyl-2-pyrrolidone.
 4. The oil-based pigmented ink compositionaccording to claim 1, wherein said (poly)alkylene glycol derivative hasa flash point of 70 to 120° C., and a boiling point of 170 to 250° C. 5.The oil-based pigmented ink composition according to claim 1, whereinsaid (poly)alkylene glycol derivative is at least one compound selectedfrom the group consisting of monoalkyl ether monoalkyl esters, dialkylethers and dialkyl esters of (poly) alkylene glycols.
 6. The oil-basedpigmented ink composition according to claim 5, wherein said(poly)alkylene glycol derivative is at least one compound selected fromthe group consisting of ethylene glycol monoalkyl ether monoalkyl ester,diethylene glycol monoalkyl ether monoalkyl ester, triethylene glycolmonoalkyl ether monoalkyl ester, propylene glycol monoalkyl ethermonoalkyl ester, dipropylene glycol monoalkyl ether monoalkyl ester,tripropylene glycol monoalkyl ether monoalkyl ester, ethylene glycoldialkyl ether, diethylene glycol dialkyl ether, propylene glycol dialkylether, dipropylene glycol dialkyl ether, ethylene glycol dialkyl esterand propylene glycol dialkyl ester.
 7. The oil-based pigmented inkcomposition according to claim 1, wherein said polymer has a solubilityin water and ethanol of 3% by weight or less.
 8. The oil-based pigmentedink composition according to claim 1, wherein said polymer is at leastone of a pigment-dispersant and a fixing resin.
 9. The oil-basedpigmented ink composition according to claim 8, wherein saidpigment-dispersant is contained in an amount of 5 to 150% by weightbased on the weight of the pigment.
 10. The oil-based pigmented inkcomposition according to claim 8, wherein said fixing resin is at leastone resin selected from the group consisting of acrylic resins,polyester resins, polyurethane resins, vinyl chloride resins andcellulose resins.
 11. The oil-based pigmented ink composition accordingto claim 8, wherein said fixing resin has a weight average molecularweight of 2,000 to 100,000.
 12. The oil-based pigmented ink compositionaccording to claim 8, wherein said fixing resin is contained in anamount of 5 to 200% by weight based on the weight of the pigment. 13.The oil-based pigmented ink composition according to any one of claims 1to 12, which has a viscosity of 2 to 15 cp at 25° C., a surface tensionof 20 to 40 mN/m at 25° C., and a dispersion average particle size of 20to 200 nm.
 14. The oil-based pigmented ink composition according toclaim 1, which is used in an ink-jet printing system.